the doctor did what he could --- the girl who was badly hurt

答案选C.动词不定式的一般式形式表示将要做的事,（医生竭尽全力）The doctor did what he could 就是为了去挽救那个在事故中严重受伤的女孩（to save the girl who was badly hurt in the accident）.
to save the girl who was badly hurt in the accident整体是动词不定式短语作状语,表示目的.
to save动词不定式；the girl是to save 的宾语；who was badly hurt in the accident是定语从句,修饰the girl.
新年快乐!

C

此处不定式

医生竭尽所能去挽救那位在事故中身受重伤的女孩儿。

the doctor did what he could --- the girl who was badly hurt in the accident
a save
b saving
c to save
d saves
选项是c
do what sb could (do) to ...的意思是：某人做了他能够做的一切去。。。